Propellant gas generator



Feb. 21, 1967 ow c ET AL 3,305,319

PROPELLANT GAS GENERATOR Filed April 2, 1965 ATTORNEYS INVENTDRS. JAMES E KOWALICK United States Patent 3,305,319 PROPELLANT GAS GENERATOR James F. Kowalick, Southampton, Pa., and William E. Perkins, Runnemede, N .11., assignors to the United States of America as represented by the Secretary of the Army Filed Apr. 2, 1965, Ser. No. 445,286 8 Claims. (Cl. 23281) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to use of any royalty thereon.

This invention relates to a propellant gas generator, and particularly to a gas generator which converts high temperature gases to lower temperature gases in a single unit.

Various means were used heretofore for converting high temperature propellant gases of a gas generator into gases having a lower temperature necessary for particular applications. A typical approach was to pass the hot gases through a porous body of a chemical coolant. The hot gases would cause the coolant to decompose either partially or entirely into gaseous components which are considerably cooler than the propellant gases. The discharging gas would be capable of being used at a desired level of temperature. Basically the apparatus used would comprise a unit having two chambers, one chamber accommodating the propellant, the other of the coolant. To enhance uniform operation an orifice plate was inserted between the chambers. This orifice would control the mass flow of the propellant gases into the coolant chamber. It was found, however, that this system was inherently ineificient since the coolant would not completely decompose after it had shrunk a certain amount. The result was that hot propellant gases were oftentimes discharged.

We have found that if the coolant used could be maintained in a compressed state throughout the burning of the propellant complete decomposition of the coolant would be realized, thus providing a more efiicient and reliable gas generator unit. Accordingly it is a primary object of the present invention to provide a gas generator for converting high temperature propellant gases into lower temperature gases in an efiicient manner by maintaining the coolant used in a compacted state during the entire operation of the device.

It is another object of the present invention to provide apparatus of the above type wherein a piston assembly acting under propellant gas pressure moves with the decomposing body of coolant to maintain it in a compact state.

A further object of the present invention is to provide an apparatus of the character described wherein the above piston assembly also acts as a metering orifice for the propellant gases.

Still another object of the present invention is to provide apparatus of the aforesaid type wherein the above piston assembly is comprised of two members separated by a resilient seal ring which all cooperate to provide an effective seal between the propellant and coolant chambers.

It is yet another object of the present invention to provide an apparatus of the above type wherein the piston assembly acts to funnel the coolant towards the axis of the apparatus for increasing the contact between the propellant gases and the coolant.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a view in elevation, and partly in cross section, of a propellant gas generator embodying the invention;

FIG. 2 is a view of FIG. 1 showing a condition thereof during operation of the invention;

FIG. 3 is a cross sectional view in elevation of one element of the present invention showing another embodi ment thereof; and

FIG. 4 is a view on the line 4-4 of FIG. 3.

Referring to the drawings, in which like reference characters refer to like parts throughout the various figures, and referring particularly to FIG. 1, 10 is a container having a closed end 12 defining a gas eXit or discharge port 14 therethrough and a closure 16 on the other end which closure 16 is held in place by means of a screw thread mating with the container 10, or the like.

The container 10 comprises two chambers, namely a high temperature chamber 18 at the closure 16 end and a low temperature chamber 20 at the opposite or discharge Dort 14 end. A propellant 22 is disposed in the high temperature chamber 18. In this embodiment the pro- Dellant 22 is a solid grain propellant but may be of any form suitable to a particular application. An igniter 24 is provided in the closure 16 for ignition of the propellant 22. Any common igniter, electrical or mechanical, may be used.

The low temperature chamber 20 contains a porous body of chemical coolant 26. This body of coolant 26 is of such a nature that it decomposes partially or wholly into gaseous products when a sufiicient quantity of heat is absorbed thereby. This type of a process or change of the coolant is commonly characterized as an endothermic reaction. Typical of a few coolants, but not limited thereto, displaying the above capability which may be used in the present invention are ammonium carbamate, ammonium carbonate and ammonium hydrosulfide. The coolant 28 selected, however, should be porous and capable of being maintained in a compact body. As the expression is used herein, compact means firmness or soundness. Thus, the coolant 26 is in the form of a firm body while also being porous. For example, a charcoal filter used with many of todays cigarettes would be a compact porous body. The porosity is necessary to allow gases to pass through the body while the firmness thereof is necessary for the most efiicient decomposition reaction.

The high temperature chamber 18 and low temperature chamber 20 are separated by a piston assembly 28 which is slidable with respect to the container 10. This assembly takes the form of a Bridgman piston having an orifice through piston elements thereof. A Bridgman piston is clearly illustrated in FIG. 20 on page 1000 of Mechanical Engineers Handbook, edited by Lionel S. Marks, fifth edition. Specifically the piston assembly 28 consists of a first element 30 which is essentially T- shaped having its broad portion facing the propellant 22 and its narrow portion 34 longitudinally oriented in a mating section 36 of a second element 38. A resilient ring 40 separates the elements 30 and 38, and functions to act as a seal between the high temperature chamber 18 and low temperature chamber 20. The ring 40 may be leather, rubber, or whatever kind of resilient material would satisfy a particular application. The forward face 42 of the second element 38 (i.e. the face directed towards the discharge port 14) contacts the body of coolant 26. This forward face 42 is preferably frustoconical in shape to provide a funnelling action on the coolant 26, the significance of which will be shown hereinafter.

A clearance space 44 is provided in the mating sec- Etion 36 between the forward end thereof and the end of the narrow portion 34 of the first element 30. This clearance space 44 enables the first element 30 to slide Iforwardly with respect to the second element 38 when =a pressure is applied to the broad portion 32 of the ifirst element 30. This pressure will, of course, be supiplied by the gases of the propellant 22. The effect of this relative sliding is to compress the ring 40 which forms a high pressure seal of the Bridgman piston type. The elements 30 and 38 define longitudinal coaxial openings 46 and 48 respectively therethrough which combine to form an interrupted orifice for metering the flow of propellant gases into the low temperature chamber 20. The pressure of the propellant 22 gases acting on the broad portion 32 is controlled by the size of the opening 46. This pressure produces a force on the first element 30 which force is dependent on the area of the broad portion 32 (i.e. force=pressure area). This force is transmitted to the ring 40. The area of the ring 40 is less than the area of the broad portion 32. Therefore, the pressure in the ring 40 material, that is, acting on the ring 40, is greater than the pressure acting on the broad portion 32. Consequently a seal is provided between the chambers 18 and 20 which is virtually leak-proof. This seal, as indicated above, is the commonly known Bridgman piston high pressure seal.

In operation, the propellant 22 is ignited producing high temperature gases which act on the piston assembly 28 to form the high pressure seal as outlined above. The gases are metered through the orifice represented by openings 46 and 48. The gases contact the coolant 26 which decomposes by the heat absorbed therefrom to form relatively low temperature gaseous products. This decomposition process results in a mixture of propellant gases and coolant 26 gaseous products having a temperature lower than that of the propellant gases. This lower temperature gas mixture passes through the porous body of coolant 26 towards the discharge port 14. During standby condition the discharge port 14 has a plug 50 therein. The plug 50 prevents any foreign matter from entering into the low temperature chamber 20. The plug 50 is oriented in the discharge port 14 to be removed therefrom when a predetermined pressure is reached in the low temperature chamber 20. After removal of the plug 50 the low temperature gas mixture proceeds to flow out of the discharge port 14, and to its preselected destination.

The propellant gases act upon that portion of the coolant 26 which it encounters immediately upon discharge from the opening 48. Intimate and direct contact between the propellant gases on a compact body of coolant 26 provides the highest degree of decomposition of the coolant 26. This contact is insured in this invention when the piston assembly 28 slides forwardly towards the discharge port 14 under the urging of the force thereon by the propellant gases. As the coolant 26 decomposes and the body thereof diminishes the piston assembly 28 continues moving forwardly, thus keeping the coolant 26 in a compacted condition while providing intimate and direct contact of the propellant gases with the coolant 26.

The frusto-conical shape of the forward face of the second element 38 tends to funnel the coolant 26 towards the longitudinal axis of the container 10, thus towards the propellant gas discharge. This funnelling effect increases the possibility of contact of the propellant gases with the coolant 26 thereby also adding to the efiectiveness of the decomposition process of the coolant 26.

The decomposition process of the coolant 22 can be made even more efficient by use of a piston assembly 28 modified as shown in FIGS. 3 and 4. Essentially this piston assembly provides in addition to a first element 30a which is substantially the same as the first element 30, a spinning element 52 capable of spinning when acted upon by the propellant gases. A resilient ring 40a separates the first element 30a and the spinning element 52. The spinning element 52 further comprises an intermediate member 54 which is only slidable in the container 10 and a forward member 56 separable from the member 54 and containing a plurality of regularly oriented slots 58 extending above the longitudinal axis of the member 54 and radially forwardly therefrom. This relationship is clearly shown in FIGS. 3 and 4. The propelalnt gases flowing through the slots 58 act on the forward member 56 causing it to spin about its longitudinal axis. The gases discharging through the slots 58 while the forward member 56 is spinning contact more area of the coolant 26, than a non-spinning element such as 38, thus resulting in a more efiicient coolant 26 decomposition. The forward face of the forward element 54 is frusto-conical in shape for funnelling the coolant as described above during movement of the piston assembly towards the discharge port 14.

Resort may be had to the various modification and variations which fall within the spirit of this invention and the scope of the appended claims.

We claim:

1. A propellant gas generator including a container defining a high temperature chamber and a low temperature chamber, said container having one closed end defining a gas discharge port from said low temperature chamber and another closed end containing propellant igniting means extending into said high temperature chamber;

a propellant in said high temperature chamber;

a compact body of porous chemical coolant in said low temperature chamber, said coolant being endothermically reactable with the combustion gases of said propellant to produce at least one gaseous product; and

piston means defining an orifice therethrough separating said chambers, said piston means contacting said body of coolant and movable in the direction of said discharge port under the pressure of said propellant combustion gases whereby a diminishing body of said coolant may be maintained constantly in a compacted condition as said coolant reacts with said propellant combustion gases.

2. A propellant gas generator including a container defining a high temperature chamber and a low temperature chamber, said container having one closed end defining a gas discharge port from said low temperature chamber and another closed end containing propellant igniting means extending into said high temperature chamber;

a propellant in said high temperature chamber;

a compact body of porous chemical coolant in said low temperature chamber, said coolant being endothermically reactable with the combustion gases of said propellant to produce at least one gaseous product;

piston means defining an orifice therethrough separating said chambers, said piston means contacting said body of coolant and movable in the direction of said discharge port under the pressure of said propellant combustion gases whereby a diminishing body of said coolant may be maintained constantly in a compacted condition as said coolant reacts with said propellant combustion gases, and

sealing means between said chambers in sealing engageinent with said container wall said sealing means being propellant gas pressure responsive for providing effective sealing between said chambers.

3. A propellant gas generator as set forth in claim 2 wherein said sealing means is contained in said piston means and moves along therewith.

4. A propellant gas generator as set forth in claim 2 wherein said gas discharge port contains closure means so constructed and arranged as to open when a predetermined pressure is reached in said low temperature chamber.

5. A propellant gas generator as set-forth in claim 2 wherein said piston means comprises first, second, and third elements separable from each other and longitudinally arranged within said container and in movable engagement therewith, said first element slidably arranged in said second element and separated by resilient sealing means in engagement with said container wall, said first element having an orifice therethrough, whereby when said propellant is ignited the pressurized gases therefrom cause said first element to slide Within said second element to compress said sealing means against said container wall creating a pressure on said sealing means greater than the pressure in said high temperature chamber, said third element having a plurality of openings therethrough arranged angularly with respect to the longitudinal angle of said third element in such a manner that when said propellant gases pass through said openings a force is directed against said third element to rotate same about its longitudinal axis.

6. A propellant gas generator as set forth in claim 2 wherein said piston means comprises first and second elements separated by resilient sealing means in engagement with said container wall, said first element slidably arranged in said second element, said elements having communicating orifices therethrough whereby when said propellant is ignited the pressurized gases therefrom cause said first element to slide within said second element to compress said sealing means against said container wall creating a pressure on said sealing means greater than the pressure in said high temperature chamber.

7. A propellant gas generator as set forth in claim 5 wherein said second element has a frusto-conical shaped face in contact with said coolant.

8. A propellant gas generator including a container defining a high temperature chamber and a low temperature chamber, said container having one closed end defining a gas discharge port from said low temperature chamber and another closed end containing propellant igniting means extending into said high temperature chamber;

a propellant in said high temperature chamber;

a compact body of porous chemical coolant in said low temperature chamber, said coolant of such a nature as to decompose into at least one gaseous product by an endothermic reaction with the gases of said propellant;

a piston assembly separating said chambers, said assembly comprising a first and second element longitudinally arranged within said container and in movable engagement therewith, said first element slidably arranged in said second element, resilient sealing means in engagement with said container wall separating said elements, said elements having communicating orifices therethrough, said second element defining a frusto-conical shaped face in communication with said coolant whereby when said propellant is ignited the pressurized gases therefrom cause said first element to slide within said second element to compress said sealing means against said container wall creating a pressure on said sealing means greater than the pressure in said high temperature chamber, and said piston assembly moves in the direction of said discharge port under the pressure of said propellant gases to maintain a diminishing body of coolant always in a compacted condition as said coolant decomposes.

References Cited by the Examiner UNITED STATES PATENTS 1/1957 Maurice et al 102-39 6/1961 Musser 23--281 

1. A PROPELLANT GAS GENERATOR INCLUDING A CONTAINER DEFINING A HIGH TEMPERATURE CHAMBER AND A LOW TEMPERATURE CHAMBER, SAID CONTAINER HAVING ONE CLOSED END DEFINING A GAS DISCHARGE PORT FROM SAID LOW TEMPERATURE CHAMBER AND ANOTHER CLOSED END CONTAINING PROPELLANT IGNITING MEANS EXTENDING INTO SAID HIGH TEMPERATURE CHAMBER; A PROPELLANT IN SAID HIGH TEMPERATURE CHAMBER; A COMPACT BODY OF POROUS CHEMICAL COOLANT IN SAID LOW TEMPERATURE CHAMBER, SAID COOLANT BEING ENDOTHERMICALLY REACTABLE WITH THE COMBUSTION GASES OF SAID PROPELLANT TO PRODUCE AT LEAST ONE GASEOUS PRODUCT; AND PISTON MEANS DEFINING AN ORIFICE THERETHROUGH SEPARATING SAID CHAMBERS, SAID PISTON MEANS CONTACTING SAID BODY OF COOLANT AND MOVABLE IN THE DIRECTION OF SAID DISCHARGE PORT UNDER THE PRESSURE OF SAID PROPELLANT COMBUSTION GASES WHEREBY A DIMINISHING BODY OF SAID COOLANT MAY BE MAINTAINED CONSTANTLY IN A COMPACTED CONDITION AS SAID COOLANT REACTS WITH SAID PROPELLANT COMBUSTION GASES. 